Employees allowed to access their corporate PCs from their home PCs using some remote access control software, does this give a route into the corporate LAN for any viruses or spyware that may be on that home computer?

Well, if the system where to become infected, it's possible... There are some viruses which can spread across a network.

A Firewall and Virus Scanner on all machines would be a good start to thwart many viruses however.